(1) Field of the Invention
This invention relates to a digitizing apparatus in which the surface of a model is traced by a probe which measures distance contactlessly, thereby forming digitizing data along the profiling path.
(2) Description of the Related Art
In ordinary tracer control, a stylus is moved while in contact with the surface of a model. Displacement quantities .epsilon.x, .epsilon.y, .epsilon.z along respective axes, which depend upon the tracing path on the model surface, are detected from a tracer head. In a tracer control apparatus, the displacement quantities .epsilon.x, .epsilon.y, .epsilon.z along the respective axes are combined into a vector and the direction of a normal to the model surface is computed to form profiling data. When machining is subsequently performed based on the digitizing data, offset values conforming to the axial components of the normal vector are decided and a difference between stylus diameter and cutter diameter is corrected by a three-dimensional correction.
In digitizing based on this conventional contact profiling system, the direction of displacement does not accurately reflect the normal line direction of the model surface due to friction between the stylus and model. It is difficult to form accurate digitizing data because of disturbance caused by roughness of the model surface. In addition, due to the inaccurate normal vector, the original model shape cannot be reproduced at the time of machining even if cutter diameter is compensated for in three dimensions.